Unwanted oxidation is harmful to the color, taste, composition and quality of wine. Prevention of oxidation and spoilage which would otherwise result from air contact is a major concern during the production and aging of quality wine, and it is a common practice to minimize such oxidation by periodically adding more wine to "top up" the barrels or containers and reduce the ullage which forms at the top of the containers as the wine volume "shrinks" due to seepage, contraction, sampling and the like. The "topping up" process is time consuming and costly and, in fact, exposes the wine to air each time the container is opened to enable addition of the "fill wine". Further, a costly variety of sizes of cooperage is required to keep the ever decreasing volume of wine in fully filled containers. Other methods have been used to reduce oxidation, such as by introducing nitrogen or carbon dioxide into the head space of partially filled containers. However, because of the penetration of oxygen and loss into the wood by diffusion, this is not successful in containers that do not have impervious walls. Olive oil has been floated on top of wine to insulate it from air in partially filled containers, but this degrades the taste of the wine and renders the barrels difficult to clean.